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Online User Guide - Adobe Photoshop

Using Mountain High Maps USA Relief


Using Masks

In image manipulation applications, masks are used as means of selecting intricate -- or simple -- areas of an image. Masks can be either solid black and white or they can be grayscale. In Photoshop, the white area of a mask is the area which will be selected, although in many situations the option to inverse the selection is just as often used. The masks are provided at both 300 pixels per inch (ppi) resolution, and are exactly the same size as their corresponding state relief maps.

Each state map folder or directory contains the mask for the state map which represents an exact outline of the state territory.

Loading Masks the Easy Way

Although the masks really come into their own when used with Photoshop's Alpha Channels, you can also use the masks to apply quick and easy selections to a map without using channel operations. Just follow these instructions:

  1. Open the base grayscale or colorized version of the state map you wish to work on - you may want to select a smaller state such as Delaware, Rhode Island or the sample map to speed processing of this exercise.

  2.  
  3. Open the corresponding state mask for the map. When working on the TIFF version of the mask, select "Grayscale" from the Mode menu. Enter a value of "1" in the Size Ratio box in the dialog which follows, and click "OK".

  4. Choose "Load Selection" from the "Select" menu. In the dialog box which opens, the "Source" pop-up menu will show the name of the state map you are working on, while the "Channel" pop-up menu will display the mask you have just opened.  Click "OK." The state outline will now appear on the map as "marching ants." This indicates the selected area.

That's it! Any action you now take will apply only to the selected portion of the map. To get an instant result, select "Adjust > Brightness/Contrast..." from the Image menu, and, with "Preview" checked, move the sliders.
 

Using Channels

The concept is really quite simple; each base color of an image has a separate channel -- RGB images have three channels (one each for the three video colors of red, green, and blue), plus one extra to show the combined colors, whereas CMYK images have four channels (one each for the four process colors), plus one showing them combined. Grayscale images only have one channel.

However, any number of new channels can be added to an image, and these provide a place where you can store masks that can be used to make selections. Using masks, you can do this as follows:

  1. Open the base version of a state map you wish to work on - you may want to select a smaller state such as Delaware, Rhode Island or the sample map to speed processing and provide faster results.

  2.  
  3. Open the "Channels" floating palette by selecting "Show Channels" from the "Window" menu. Click on the right-pointing arrow at top right of the Channels palette and select "New Channel."

  4.  
  5. In the dialog box which appears, name the channel "State mask" and click "OK" (leave the other settings as they are). The map image window will now go blank, this being an "empty" new channel.

  6.  
  7. Open the corresponding state mask for the map you are using, and choose "All" from the "Select" menu.

  8. Then, either
     

  9. Holding the mouse button down, drag the mask either from its document window onto the window of the channel you just created, or drag it directly from the "Channels" palette onto the document (if you use the latter method you do not need to create a channel first--dragging the source channel onto the document automatically creates a new channel).

  10. Or:
     

  11. Choose "Copy" from the "Edit" menu, and close the state mask window. The base map window showing the blank channel should now be active (if not, just click anywhere within it). Choose "Paste" from the "Edit" menu. This will paste the state map mask into the blank channel.

  12. Whichever method you use (steps 5 or 6), the result is the same, except that the latter uses more memory.

    You will now use the "State mask" channel to create a selection for manipulating your base state map image. The important thing to remember about using channels for selections is that the black areas on the mask channel are those that will remain unaffected on the channel you are manipulating. Or, to put it another way, the white areas of the mask are those which will be affected when you make changes to your image. To manipulate your image:
     

  13. Click on the word "Black" on the Channels palette (or hit "Command-1" (Mac) or "Ctrl+1" (PC) on the keyboard"). This will display the base map channel.

  14.  
  15. Choose "Load Selection" from the "Select" menu. In the dialog box which appears, check the "Invert" button and click "OK." The state outline will appear as "marching ants." This indicates the selected area.

  16.  
  17. Choose "Adjust > Brightness / Contrast..." from the "Image" menu. In the dialog box that opens, move the slider triangle on the Brightness bar until "+95" is displayed in the value box.

  18.  
  19. Click "OK." The map will now show the state in a much paler shade of gray, creating a contrast between state area and the surrounding states area:
MHMtip CONTRAST LEVELS
The grayscale relief maps in the Mountain High Maps USA Relief collection have been engineered to use the fullest range of gray levels that PostScript can achieve--256. This provides you with the greatest flexibility for customizing the maps. However, you may find that using the maps as they come, straight off the disc (right), makes it difficult to read any information such as text annotations, so you may have to alter the contrast of the relief maps. Photoshop provides many methods for adjusting contrast, but the most flexible is the "Levels" control ("Image > Adjust" menu), and a few examples of various settings are shown below.
INPUT: 0 - 1.00 - 100
OUTPUT: 0 - 255
INPUT: 0 - 1.00 - 100
OUTPUT: 128 - 255
INPUT: 0 - 1.00 - 100
OUTPUT: 200 - 255
INPUT: 0 - 1.00 - 255
OUTPUT: 70 - 255
INPUT: 0 - 1.00 - 255
OUTPUT: 128 - 255
INPUT: 0 - 1.00 - 255
OUTPUT: 200 - 255
INPUT: 0 - 3.00 - 255
OUTPUT: 0 - 200
INPUT: 0 - 4.00 - 200
OUTPUT: 0 - 200
INPUT: 0 - 4.00 - 128
OUTPUT: 0 - 220
INPUT: 0 - 1.00 - 255
OUTPUT: 70 - 180
INPUT: 0 - 1.00 - 255
OUTPUT: 128 - 200
INPUT: 0 - 1.00 - 255
OUTPUT: 180 - 220

Applying effects to selections

The technique of using a selection channel can be employed for a large number of effects.

If, for example, after step 8 above, you pressed the delete key, you would delete the selected area to reveal the background color, ending up with a white area outside the state. However, if you hold down the "Option" or "Alt" key while hitting "delete," the state area will fill with the foreground color.

You can fill the area outside the state with a gray tint by defining a tint of black. Do this by opening the "Picker" palette and using the slider triangle on the "K" bar until it displays the desired percentage.

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